Well, PythonEggs sounded like a neat idea, and now they've made it possible to turn Trac's pluggable framework into a real plugin system. Simply stick your extensions into an Egg, create a "plugins" directory in your environment, and drop-in the file.
Jonas is developing a webadmin module for Trac as a plugin, and I took his example and have repackaged my account management module. Turning it into a plugin was quite trivial, but there are a couple of other things I'd like to clean up tomorrow before I release it.
The Trac documentation should be updated soon to explain how to make plugins.